The present invention relates to a laser machining apparatus and, particularly, to such an apparatus which can perform high-quality, high precision cutting of objects such as sharply angled portions of a plate-type workpiece in a complex configuration with minimum burn-through loss of material due to thermal saturation.
FIG. 1 shows schematically in cross section a conventional laser machining apparatus of this type. In FIG. 1, a laser beam 3 generated by a laser oscillator 2 and delivering a laser beam transmission tube 4 is deflected by a fully reflecting mirror 5 such that the beam is directed to a workpiece 1 at a right angle. Then, the beam 3 is condensed by a condenser lens 7; the condensed beam irradiates the workpiece 1 through a machining head 6.
An assist gas introduced through a gas port 8 into the machining head 6 is jetted from a nozzle 9 to the workpiece 1 to assist the laser machining thereof. The workpiece 1 is supported by a machining table 10 which is movable two-dimensionally by X and Y drive motors 11a and 11b. With this arrangement, laser cutting along a complex path is possible.
In the conventional laser machining apparatus, since the magnitude and waveform of the laser output are fixed, fine portions of the workpiece which are laser-cut tend to be subjected to varying thermal influences, resulting in nonuniformity of quality and low precision of the cutting operation.
FIG. 2 illustrates an example of a workpiece cut using the conventional laser machining apparatus. In FIG. 2, around sharp edge portions a, b and c where the direction of cutting is changed, the real velocity, i.e., the relative velocity (m/min), of the laser beam 3 irradiating the workpiece 1 with respect to the latter, is unavoidably lower than along straight edge portions, as shown in FIG. 3. Therefore, because machining is performed with a constant laser output, such sharply edged portions as the portions a, b and c or finely configurated portions such as portions i and j tend to be overheated, and thus portions 15 (hatched regions) of the workpiece material are removed (melting loss) due to thermal saturation of these portions.
To avoid this problem, the operator of the laser machining apparatus has had to determine optimum cutting conditions for every cut performed on the material, taking into account the thickness and cutting path of the workpiece, which is troublesome and requires time-consuming work and with the degree of success depending largely on the operator's skill.